Large, flexible polymeric sheets, which are often referred to as membranes or panels, are used in the construction industry to cover flat or low-sloped roofs. These membranes provide protection from the environment particularly in the form of a waterproof barrier. As is known in the art, commercially popular membranes include thermoset membranes such as those including cured EPDM (i.e. ethylene-propylene-diene terpolymer rubber) or thermoplastics such as TPO (i.e. thermoplastic olefins).
These membranes are typically delivered to a construction site in a bundled roll, transferred to the roof, and then unrolled and positioned over the roof surface. The sheets are then secured to the building structure by employing varying techniques such as mechanical fastening, ballasting, and/or adhesively adhering the membrane to a roof substrate. The roof substrate to which the membrane is secured may be one of a variety of materials depending on the installation site and structural concerns. For example, the roof substrate surface may be a concrete, metal, or wood deck, it may include insulation or recover board, and/or it may include an existing membrane.
In addition to securing the membrane to the roof—which mode of attachment primarily seeks to prevent wind uplift—the individual membrane panels, together with flashing and other accessories, are positioned and adjoined to achieve a waterproof barrier on the roof. Typically, the edges of adjoining panels are overlapped, and these overlapped portions are adjoined to one another through a number of methods depending upon the membrane materials and exterior conditions. For example, a seam can be prepared by applying a liquid adhesive or a solid tape. Or, where the membranes are thermoplastic, a seam can be formed by heat welding adjacent overlapping membranes.
Where the membranes are adhesively secured to a roof substrate, several modes of adhesive attachment are known. One attractive mode includes the use of a pre-applied (i.e. factory-applied) adhesive, which may be covered by a release member, that is applied to the surface of the membrane. These membranes, which are commonly referred to as peel-and-stick membranes, may employ a variety of adhesive compositions, including those applied as a hot melt, including styrene-ethylene-butylene-styrene (SEES), butyl-based adhesives, EPDM-based adhesives, acrylic adhesives, styrene-butadiene adhesives, polyisobutylene adhesives, and ethylene vinyl acetate adhesives.
While peel-and-stick membranes have been used commercially, attempts to use the factory-applied adhesive for seaming adjacent membranes to one another is problematic. The seams between membranes are exposed to conditions not typically present under the membrane (i.e. where the membrane is attached to the underlying substrate), and it is believed that these factors lead to the failure of seams formed using the same pressure-sensitive adhesives used to secure the membrane to the roof surface. For example, as disclosed in U.S. Publ. No. 2004/0191508, it is believed that temperature swings and moisture contributes to the premature failure of these seams. As a result, thermoplastic peel-and-stick membranes are often manufactured with an “open lap region” (i.e. a lap area without an adhesive layer), along the lap edge, so that the seams of these thermoplastic membranes can be heat welded. Alternatively, as disclosed in U.S. Publ. No. 2010/0024955, adhesive tapes (such as butyl-based adhesive tapes) are factory-applied along the lap edge in lieu of the pressure-sensitive adhesive applied to the remainder of the membrane. It has also been proposed, although with limited success, to factory prime the upper surface of the adjoining membrane in an attempt to improve the seam.
Nonetheless, when peel-and-stick membranes are installed, the prevailing preference is to heat seam adjacent membranes while allowing the factory-applied adhesive to secure the membrane to the roof surface. As suggested above, this can be achieved where an “open lap region” is provided during manufacture of the composite. There are, however, difficulties encountered even where an “open lap region” is provided. For example, an “open lap region” is only useful where a full-width sheet is employed. In those situations where the width of the sheet must be altered, the factory-fabricated “open lap region” is lost. These same difficulties can be encountered where the length of the roofing composite is altered during installation.
In order to alleviate these problems, some contractors have found it useful to remove the adhesive layer within the lap region during installation. This has been accomplished by mating a high-tensile member (such as a fabric-backed adhesive tape) to the adhesive layer within the lap region, and then forcefully removing the high-tensile member to thereby remove the underlying adhesive layer. In order to accomplish this procedure, the release member must be removed in the lap region. Accordingly, contractors have found it useful to cut the release member along the lap region and subsequently remove a portion of the release member. Problems have also been encountered because the forceful removal of the high-tensile member can also cause removal of the adhesive layer in an area outside of the lap region. This is believed to be caused by the adhesive having higher internal strength relative to the bond strength to the membrane, and therefore the removal of the adhesive takes place lateral to where the high-tensile member is mated to the adhesive. As the skilled person will appreciate, where the adhesive layer is unnecessarily removed from the non-lap portions of the membrane, the ability to adequately secure the membrane to the roof surface can be compromised. Another problem that can be encountered is damage to the membrane while cutting the release member. Specifically, contractors have found it useful to cut the release member with a construction knife, and therefore the depth to which the blade of the knife is inserted into the adhesive layer and potentially into the membrane is subject to contractor skill. Since the thickness of the adhesive layer is typically less than 1,000 μm, great demands are placed on the contractor to avoid cutting the membrane.